Contact lenses made from silicone hydrogels are rapidly gaining popularity over contact lenses made from conventional hydrogel materials because, like conventional hydrogel lenses, they are comfortable to wear, but they have the added advantage of having higher oxygen permeability, which is believed to be healthier for the eye. However, contact lenses made from silicone hydrogels typically need to be washed in volatile organic solvents to extract unreacted components from the lenses. The use of volatile organic solvents in manufacturing presents safety and environmental concerns and adds costs to the manufacturing process. Efforts have been made to develop silicone hydrogel formulations that can be adequately washed in water without the use of volatile organic solvents. However, certain lens formulations result in lenses with surface distortions after being washed in water. Additional wet-processing methods that do not employ volatile organic solvents are desirable for manufacturing distortion-free contact lenses.
Some patent documents describing wet-processing methods of silicone hydrogel contact lenses include U.S. Publ. No. 2007/0228585, U.S. Publ. No. 2007/138668, U.S. Pat. No. 6,765,083, U.S. Publ. No. 2004/0091613, and U.S. Publ. No 2012/0220689.